The medical device industry produces a wide variety of electronic and mechanical devices for treating patient medical conditions such as pacemakers, defibrillators, neuro-stimulators and therapeutic substance delivery pumps. Medical devices may be configured to be surgically implanted or connected externally to the patient receiving treatment. Clinicians use medical devices alone or in combination with therapeutic substance therapies and surgery to treat patient medical conditions. For some medical conditions, implantable medical devices provide the best and sometimes the only therapy to restore an individual to a more healthy condition and a fuller life.
An implantable neurological stimulation system may be used to treat conditions such as pain, movement disorders, epilepsy, depression, pelvic floor disorders, gastroparesis, and a wide variety of other medical conditions. Such a neurostimulation system typically includes an implantable neurostimulator, a medical electrical stimulation lead, and an extension such as that shown in the Medtronic, Inc. brochure “Implantable Neurostimulation System” (1998). More specifically, the neurostimulator system may be an Itrel II® Model 7424 or an Itrel 3® Model 7425 available from Medtronic, Inc. of Minneapolis, Minn. that may be used to treat conditions such as pain, movement disorders and pelvic floor disorders. The neurostimulator is typically connected to a stimulation lead that has one or more electrodes to deliver electrical stimulation to a specific location in the patient's body.
Some therapies involve electrical stimulation of the brain and others involve stimulation of the spinal cord. Still other therapies involve electrical stimulation of other sites in the patient's body.
Among the various types of implantable medical electrical leads employed to treat pain by electrically stimulating a patient's spinal cord or portions thereof are the Medtronic PISCES QUAD Model No. 3487A and PISCES Z QUAD Model No. 3890, 3891 and 3892 medical electrical leads. These leads are designed to be percutaneously introduced near a patient's spinal cord, and aid in the management of chronic, intractable pain via pulsed electrical stimulation through nerve structures in the dorsal aspect of the spinal cord. Activation of the stimulated structures produces nerve impulses that often inhibit the transmission of pain.
Currently commercially available PISCES leads have four platinum iridium electrodes mounted on the distal ends of the leads. Each electrode is 3 mm long and is spaced 6 mm from the adjacent electrode(s). Each PISCES electrode has a ring shape and extends around the circumference of the lead body. At the proximal end of a PISCES lead is an in-line four-conductor connector for mechanical and electrical attachment to a lead extension or an implantable stimulator. Each electrode thus has a single unique electrical conductor associated with it.
Experience with the PISCES series of leads has shown that intraoperative stimulation tests and lead position adjustments should generally be performed on a patient to ascertain optimal lead position and orientation. Various electrode configurations, locations and orientations are tested to obtain appropriate parasthesia during surgery, repositioning the lead as necessary. Certain precautions may be taken during surgery to minimize the risk that lead position will shift post-operatively, such as anchoring the distal portion of the lead with non-biodegradable sutures to the supra-spinous ligament or deep fascia. Despite careful testing, positioning and anchoring of percutaneously spinal cord stimulation leads during surgery, however, in some patients inadequate or minimal therapeutic effect is nevertheless obtained. In still other patients, leads may shift position post-operatively, resulting in inadequate or no parasthesiatic effect.
Segmented electrodes (also referred to as segments herein), which are electrodes that do not extend around the full circumference of the lead body at the point of stimulation (e.g., may extend anywhere from about 1 degree of arc to about 359 degrees of arc), may be desired for targeted stimulation or for efficient use of energy. For example, for deep brain stimulation it may be desirable to stimulate on only one side of the lead while avoiding stimulation on the other side (in which case a single segment of about 180 degrees may be one solution). Or it may be desirable to stimulate on one side of the lead under certain conditions and the other side under different conditions or at a different time (one solution for this may be to have two or more segments each of 60, 100, 120 or 160 degrees of arc (for example) at the same axial position or location on the lead).
One concern with segmented medical leads is the interaction between the electrode and the lead body. Ring shaped electrodes used for non-segmented electrodes do not generally share this problem because the ring shape holds the electrode to the lead body. Lead failure by a segmented electrode pulling away from the lead body is cause for concern. Such a failure not only possibly results in an inoperative lead, but also presents the significant problem of how to remove the lead from the patient's body without harming surrounding tissue. A lead is desired that solves this problem and is easily manufactured.
The foregoing and other features and advantages, which will now become more readily apparent by referring to the following specification, drawings and claims, are provided by the various embodiments of the present invention.